1. Field of the Invention
Priority is claimed on Japanese Patent Application No. 2007-154017, filed Jun. 11, 2007, the contents of which are incorporated herein by reference in their entirety.
The present invention relates to an airbag apparatus which is provided at, e.g., a steering wheel of a vehicle, and develops an airbag when an impact is applied to the vehicle, in order to protect a passenger.
2. Description of the Related Art
There are disclosures of airbag apparatuses which develop an airbag using high-pressure gas provided from are inflator, at a time of a vehicle impact or the like. Some of such airbag apparatuses are provided with a vent hole, which is released in the process of the development of the airbag.
Some airbag apparatuses have an airbag provided with rupture joining parts which rupture in the process of the airbag development, in order to control the airbag development behavior and the internal air pressure thereof. At the time of the inflating operation, the rupture joining parts are ruptured part by part, thereby gradually increasing the volume of the airbag (e.g., see Japanese Unexamined Patent Application, First Publication No. 2006-224748).
In the airbag apparatus disclosed in the Japanese Unexamined Patent Application, First Publication No. 2006-224748, a plurality of the rupture joining parts are provided at the peripheral part of the airbag. The plurality of the rupture joining parts are rotationally symmetric to each other. A part of one rupture joining part overlaps with another rupture joining part in the circumferential direction. A strip-shaped vent hole cover which covers the vent hole is secured to the airbag, by a part of the rupture joining part. In this airbag apparatus, a gas inlet connected to the inflator is provided at the center part of the airbag. When the inflator is operated, the airbag develops, starting from the center part thereof, expanding in radially outward directions. During this, the rupture joining parts are ruptured starting from a starting-end thereof provided at a center part of the airbag, to the finishing-end thereof provided at an outer part of the airbag, continuously. The vent hole cover is secured at a position corresponding to the middle part between the starting-end and the finishing-end of the rupture joining part. During the outward expansion in the development of the airbag, the attachment of the vent hole cover to the airbag is released, and the vent hole is released open.
Therefore in this airbag apparatus, during the inflating operation, since the rupture joining part is ruptured gradually, the airbag development behavior and the internal air pressure can be controlled appropriately. During the rupture of the rupture joining part, by releasing the attachment of the vent hole cover, the increase of the internal gas pressure can be regulated at an appropriate timing.
As shown above, in the conventional airbag apparatus, during the inflating operation, the rupture joining part is ruptured from the center part of the airbag to the outer part of the airbag. During this, the attachment of the vent hole cover is released. If the rupture process of the rupture joining part is stopped before it reaches the part where the vent hole cover is attached for any reason, there is a problem in that the vent hole can not be released at the predetermined appropriate timing.
In view of the above problem, the object of the present invention is to provide an airbag apparatus which can release the vent hole at a predetermined timing even when the rupture of the rupture joining part is interrupted for any reason, and thereby can stably control the development behavior and the internal air pressure of the airbag.